Comparison of Conventional and Wavelet Transform Techniques for Fusion of Irs-1c Liss-iii and Pan Images

Image fusion is a technique of obtaining high spatial resolution multispectral images from low spatial resolution multispectral and high spatial resolution panchromatic images. Various techniques exist to perform such fusion. These techniques, however, do not seem to preserve the spectral information content of original multispectral image in the fused image. Hence, in this study a recent and efficient technique of fusion based on wavelet transformation was attempted and its efficiency was compared with that of the conventional techniques. Accordingly, a lower resolution multispectral image (IRS-1C LISS-III) and a high resolution panchromatic (IRS-1C PAN) were fused using three conventional techniques: IHS (Intensity Hue and Saturation), PCA (Principal Component Analysis) and Brovey Transformation and the recently evolved wavelet transformation technique. The four outputs were evaluated using visual comparison, statistical correlation (using AOI and image to image correlation) and spectral separability studies. Among the conventional methods, PCA based fusion was found to be better than IHS and Brovey transformation techniques in improving visual interpretability and in preserving the original spectral information content. When compared with conventional techniques, the wavelet transformation technique proved to be a better option since it preserved most (85%) of the spectral information content and also improved visual appreciation. Spectral separability between five land cover classes was also highest for the wavelet transformation technique. It is believed that, since wavelet transformation operates in the frequency domain, it is able to preserve most of the original image content in a better fashion than the conventional techniques, which operate in the spatial domain. Hence, it is suggested that image fusion be attempted in the frequency domain.